Abstract [en]

Background: An open observational study was performed to investigate changes in the rectal flora and antibiotic susceptibility among faecal bacteria in patients treated with antibiotics for acute intra-abdominal infection. Methods: One hundred and forty patients with acute intra-abdominal infection requiring antibiotic treatment and hospitalization were included. Eight surgical units from the southern part of Sweden participated, between January 2006 and November 2007. Antibiotic treatments were according to local guidelines. Rectal swabs were obtained on admission (sample 1) and 2-14 days after the end of antibiotic treatment (sample 2). Aerobic bacteria and yeasts were analysed. The material was divided into 2 groups: 1 group with Enterobacteriaceae and 1 group with non-fermentative Gram-negative bacteria. The susceptibility to antibiotics in each group was compared between samples 1 and 2. Results: The main finding of this study on patients with severe intra-abdominal infections was a shift in the aerobic faecal flora following antibiotic treatment, from Escherichia coli to other more resistant Enterobacteriaceae, Enterococcus faecium, and yeasts. The susceptibility to cephalosporins and piperacillin-tazobactam decreased in Enterobacteriaceae. Conclusions: Following antibiotic treatment, a shift in the aerobic rectal flora to species with intrinsic antibiotic resistance was observed. This indicates that the emergence of resistance is not due to new mutations, but rather to selection of more resistant species. This should be taken into account when designing treatments for secondary intra-abdominal infections.

Abstract [en]

Healthcare-associated infections (HAI) are important causes of mortality and morbidity, and antibiotic treatment is often necessary. Development and availability of new antibiotics are closely followed by development of resistance among microorganisms. During antibiotic therapy, a fraction of the antibiotic given is found in the gut. The human gut is an important reservoir of bacteria. Microorganisms residing or passing the gut is referred to as the gut flora or microbiota. The results of this thesis showed spread of Enterococcus spp between patients on a general intensive care unit, causing septicaemia. After improved hygiene, reorganisation of rooms and thorough cleaning of the unit, together with revision of antibiotic strategy, the incidence of septicaemia with Enterococcus spp fell. Investigation of patients treated for acute intra-abdominal infections showed a shift in the aerobic faecal flora from antibiotic-susceptible Enterobacteriaceae spp towards Enterococcus faecium, yeasts and species of Enterobacteriaceae more resistant to antibiotics, after antibiotic treatment and hospital care. Investigation of recurrent outbreaks of Serratia marcescens sepsis in patients admitted to a neonatal intensive care unit showed different clones with each outbreak. Multiple hygiene interventions and revision of antibiotic strategy subsequently obviated recurrent outbreaks of sepsis, but spread of S. marcescens was not reduced until compliance with basic hygiene guidelines remained stable above 80%. We also found that low gestational age at birth, ventilator treatment and central venous or umbilical catheters are independent risk factors for late onset sepsis. Investigation of the faecal microbiota in patients with acute appendicitis or diverticulitis revealed that disturbance of the faecal microbiota already existed on admission, with higher numbers of Enterobacteriaceae and less Bacteroides, Faecalibacterium, Ruminococcus and Prevotella prior to antibiotic treatment and hospitalisation, than the control population. After treatment and hospitalisation diversity increased significantly in the diverticulitis group, approaching the healthy controls in composition.